Conformational differences of β-tubulin between a GMPCPP and a GDP-taxol microtubule. (A–C) Contour plots at the middle of β-tubulin (see Fig. 1 A for the sectioning plane). Both the 8.8-Å (A) and low-pass–filtered 10-Å (B) maps are presented for the GMPCPP microtubule. The low-pass–filtered 10-Å map is presented for the GDP-taxol microtubule (C). The contour level of the outermost green shell is adjusted at 1.4 σ for all three maps. (D) Statistical significance of differences (t map) between the low-pass–filtered GMPCPP and GDP-taxol microtubules with a 10-Å cutoff. Red and blue show increases and decreases in the GMPCPP microtubule, respectively. Dark colors, light colors, and the mesh show significance levels of P < 10−4, P < 10−3, and P < 10−2, respectively. Arrowheads indicate OCs. Bars, 2 nm.
